To surely melt a fuse with a heating resistor, even if the voltages of the batteries incorporated in a battery pack fluctuate sharply, and to surely prevent damages to the heating resistor.

A protective element is provided with a low-fusing-point metal 5 that is fused when heated, and the heating resistor 4 that is thermally coupled to heat the low-fusing-point metal 5 by the Joule heat generated by a current that is conducted. The heating resistor 4 comprises a plurality of shunt circuits 4A connected in parallel. Each of the shunt circuits 4A is provided with a resistance element 7, having different electrical resistance. A current control element 8 is connected, in series with the resistance element 7 in at least one of the shunt circuits 4A. The current control element 8 is an element, whose electrical resistance is caused, to change by temperature or a current to control the currents of the shunt circuits 4A. If a predetermined voltage is supplied to the heating resistor 4 of this protective element; the current control element 8 controls the currents flowing through the shunts circuits 4A, and the low-fusing-point metal 5 is heated and fused by the Joule heat of the resistance element 7.